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Dissertation
Theory of laser-induced ultrafast structural changes in solids
(2010-04-21)
The present thesis is a contribution to the study of laser-solid interaction.
Despite the numerous applications resulting from the recent use of laser technology, there is still a lack of satisfactory answers to theoretical questions regarding the mechanism leading to the structural changes induced by femtosecond lasers in materials.
We provide here theoretical approaches for the description of the structural response of different solids (cerium, samarium sulfide, bismuth and germanium) to femtosecond laser ...
Dissertation
Theory of Vesicle Motion and Interpretation of Electrophysiological Experiments in Chromaffin Cells, Hippocampal Neurons and Neuromuscular Junctions
(2018-07-16)
Communication among secretory cells, neurons and other related cells is accompanied by a
process called exocytosis, which consists in the release of neurotransmitters into the intercellular space. The neurotransmitter molecules are transported inside vesicles, which move
towards the cell membrane. Once at an active site of the membrane, vesicles can undergo
fusion with the membrane. As a result of fusion, a pore in the membrane is produced, through
which neurotransmitter molecules leave the cell. Exocytosis is ...
Dissertation
Excitation of Phonons in Solids and Nanostructures by Intense Laser and XUV Pulses and by Low Energy Atomic Collision
(2016-02-17)
Intensive, ultrakurze Laserpulse regen Festkörper in einen Zustand an, in dem die Elektronen hohe Temperaturen erlangen, während das Gitter kalt bleibt. Die heißen Elektronen beeinflussen das sog. Laser-angeregte interatomare Potential bzw. die Potentialenergiefläche, auf der die Ionen sich bewegen. Dieses kann neben anderen ultrakurzen Prozessen zu Änderungen der Phononfrequenzen (phonon softening oder phonon hardening) führen. Viele ultrakurze strukturelle Phänomene in Festkörpern hängen bei hohen Laseranregungen ...
Aufsatz
Theory for the optical properties of small Hg_n clusters
(1991)
The static and dynamical polarizabilities of the Hg-dimer are calculated by using a Hubbard Hamiltonian to describe the electronic structure. The Hamiltonian is diagonalized exactly within a subspace of second-quantized electronic states from which only multiply ionized atomic configurations have been excluded. With this approximation we can describe the most important electronic transitions including the effect of charge fluctuations. We analyze the polarizability as a function of the intraatomic Coulomb interaction ...
Aufsatz
Theory for the change of bond character in divalent-metal clusters
(1991)
To determine the size dependence of the bonding in divalent-metal clusters we use a many-electron Hamiltonian describing the interplay between van der Waals (vdW) and covalent interactions. Using a saddle-point slave-boson method and taking into account the size-dependent screening of charge fluctuations, we obtain for Hg_n a sharp transition from vdW to covalent bonding for increasing n. We show also, by solving the model Hamiltonian exactly, that for divalent metals vdW and covalent bonding coexist already in the dimers.
Dissertation
Ab initio Molecular Dynamics Simulations of the Structural Response of Solids to Ultrashort Laser and XUV Pulses
(2015-04-10)
The theoretical model and underlying physics described in this thesis are about the interaction of femtosecond-laser and XUV pulses with solids. The key to understand the basics of such interaction is to study the structural response of the materials after laser interaction. Depending on the laser characteristics, laser-solid interaction can result in a wide range of structural responses such as solid-solid phase transitions, vacuum phonon squeezing, ultrafast melting, generation of coherent phonons, etc. During my ...
Aufsatz
Slave-boson approach to the size-dependent transition from van der Waals to covalent bonding in Hg_n clusters
(1994)
We use a microscopic theory to describe the dynamics of the valence electrons in divalent-metal clusters. The theory is based on a many-body model Harniltonian H which takes into account, on the same electronic level, the van der Waals and the covalent bonding. In order to study the ground-state properties of H we have developed an extended slave-boson method. We have studied the bonding character and the degree of electronic delocalization in Hg_n clusters as a function of cluster size. Results show that, for ...
Aufsatz
Unrestricted hartree-fock calculation of the ionization potential of small Hg_n clusters
(1993)
The ionization potential of small Hg_n clusters has been calculated. For the first time good agreement with experimental results has been obtained. It is shown that interatomic Coulomb interactions are important. The energy of Hg_n^+ is calculated using the unrestricted inhomogeneous Hartree-Fock approximation. As a consequence of a change in the charge distribution in Hg_n^+ , we obtain an abrupt change in the slope of the ionization potential at the critical cluster size n_cr ~ 14. The presented results are expected ...